Liquid crystal display and driving method thereof

ABSTRACT

The present invention discloses a liquid crystal display and a driving method thereof to speed up a bend alignment at an initial operation such as right after power on in the liquid crystal display with OCB mode. According to the present invention, the LCD, which includes a LCD panel, a source driver outputting image signals and a gate driver sequentially outputting scanning signals, at an initial operation, is controlled to output external bias voltages to common electrode lines and simultaneously to stop the driving of the gate driver and the source driver, according as a first time passes, is controlled to output specific common electrode voltages thereto instead of the external bias voltages and simultaneously to perform a driving of the source driver and the gate driver. As a result, at an initial operation, by applying high-level bias voltages instead of the common electrode voltages to the common electrode lines and simultaneously stopping the driving of the gate driver, the source driver and a back light, the speed of the initial bend alignment of a liquid crystal with OCB mode can be made to be high.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a liquid crystal display and drivingmethod thereof, and more specifically, to a liquid crystal display anddriving thereof to highly increase the speed of bend alignment atinitial operation such as right after power application in a liquidcrystal display with an OCB mode.

(b) Description of the Related Art

In general, since a liquid crystal display (LCD) is much thinner, muchlight-weighted and less consumed in power than a cathode ray tubeprevailing in an image display device at present, it is alreadywide-used as an image display device of portable information devicessuch as a mobile phone and a notebook computer, and it is so small inradiation of an electromagnetic wave that it is expected to prevail inan image display device for table instead of the cathode ray tube.

Such an LCD has a disadvantage that a viewing angle feature of changingbrightness and color is large depending on a direction where a screen isseen. Several methods to overcome this advantage have been proposed.

For example, a method, which increases an orthogonal brightness morethan 30 percent by attaching a prism plate to surface of lighttransmitting plate to increase traveling straight of an incident lightin order to improve the viewing angle of an LCD, has been put topractical use, and another method, which attaches a negative opticalcompensating plate to surface of light transmitting plate to increasethe viewing angle, is being used.

In addition, owing to an In Plane Switching mode, a wide viewing anglealmost equal to a CRT level is accomplished because a viewing angle inall direction is 160°, but it is so low in an aperture rate that it isneeded to improve this.

Besides the above methods, a variety of trials to improve a viewingangle are being made by driving methods such as OCB (Optical CompensatedBirefringency) method, PDLC (Polymer Dispersed Liquid Crystal) methodand DHF (Deformed Helix Ferroelectric) method by a TFT.

Especially, since the OCB mode has advantages that response speed ofliquid crystal is high and its viewing angle is wide, it is vigorouslyin the process of research and development.

An operation of the above OCB mode will be described in brevity withreference to FIG. 1.

FIG. 1 is a diagram to illustrate an operation of a normal OCB mode, andFIG. 2 is a diagram to illustrate ON/OFF cycle of the OCB mode.

Referring to FIG. 1, an initial alignment state of the liquid crystalthat poses between an upper plate electrode and a lower plate electrodeis a Homogeneous state (hereinafter referred to as “H”). When a specificvoltages is applied to the upper/lower plate electrode, its state ischanged through a Transient splay (hereinafter referred to as “T”) andan Asymmetric splay (hereinafter referred to as “A”) to a Bend state(hereinafter referred to as “B”), and then it works as an OCB mode.

As shown in FIG. 1, generally, an OCB liquid crystal cell is made tohave pretilt angle of about 3°˜20° in the vicinity of alignment film,the thickness of the liquid crystal cell is made to be 4˜10 μm and thealignment film is made to be rubbed in the same direction. Since thearrangement of the liquid crystal molecules in the center of the liquidcrystal layer is symmetry for left and right side, a tilt angle becomes0° below a specific voltages, and 90° over a specific voltages.Therefore, by applying a large voltages to the liquid crystal, it ismade to be 90° for tilt angle of liquid crystal molecules in the centerof liquid crystal layer, and by changing the voltages applied thereto, atilt of vicinity of the alignment film and liquid crystal molecules inthe middle layer except for the liquid crystal molecules layer in thecenter of the liquid crystal layer is made to be changed, and thuspolarization of the light transmitting through the liquid crystal layeris modulated.

Although it typically takes several seconds for tilt angle to arrangefrom 0° to 90°, the OCB liquid crystal cell has a feature that responsetime is very short such an extent of 10 ms because of voltages changethereafter with no back-flow and a bend transformation with an highelastic coefficient.

As shown in FIG. 2 a, in the ON state of normal OCB mode, its change israpid from T to A and is relatively rapid from T to B, but is slow fromA to B, as also shown in FIG. 2 b, in the OFF state of normal OCB mode,its change is slow from B to H, but is rapid from T to H or from A to H.

As described above, there is a problem that it takes a certain time toobtain a bend alignment for an OCB mode. In particular, there is aproblem that it is possible to use an LCD, by applying a large voltagesthereto for a short time after turning on a power switch of a PC monitoror a TV to have to induce bend alignment transition for the whole panelof the LCD panel.

SUMMARY OF THE INVENTION

The technique and object of the present invention is to solve the aboveproblems, and an object of the present invention is to provide a liquidcrystal display to highly increase the speed of a bend alignment in theLCD with an OCB mode at an initial operation.

In addition, further object of the present invention is to provide amethod for driving an LCD to highly increase the speed of bend alignmentat an initial operation such as right after power application in the LCDwith an OCB mode.

The LCD has an LCD panel, a source driver outputting image signals tothe LCD panel and a gate driver sequentially outputting scanning signalsto the LCD panel. At the same time of power on, high-level bias voltagesare controlled to be applied to common electrode lines of the LCD, andsimultaneously the driving of the source driver and the gate driver isstopped, and according as a specific time has passed, common electrodevoltages are controlled to be applied to the common electrode lines ofthe liquid crystal display instead of the bias voltages, and the sourcedriver and the gate driver are controlled to be driven.

Here, the LCD panel have a liquid crystal with an OCB mode.

In addition, the high-level bias voltages may be provided from anexternal device, or generated on the basis of the supply voltagesprovided to the gate driver.

Furthermore, an LCD according to another feature to implement the aboveobject comprises:

a LCD panel including a plurality of gate lines, a plurality of sourcelines crossing with the gate lines, and common electrode lines;

a back light unit located in one side of the LCD panel to output aspecific light thereto;

a back light unit located on one side of the LCD panel to output aspecific light to the LCD panel;

an inverter outputting a back light voltages for driving the back lightunit;

a switching unit first-switching the output of at least one of gatevoltages for scanning signals, data voltages for image signals anddriving voltages for the back light voltages, and second-switching theoutput of one of bias voltages and common electrode voltages; and

a timing controller, at the same time of power on, outputting a firstswitching signal for controlling the first switching operation to theswitching unit to stop the output of the gate voltages, the datavoltages and the driving voltages, and outputting a second switchingsignal for controlling the second switching operation to the switchingunit to control the output of the bias voltages, and, according as aspecific time has passed, outputting a first switching signal forcontrolling the first switching operation to the switching unit tocontrol the output of the gate voltages, the data voltages and thedriving voltages, and outputting a second switching signal forcontrolling the second switching operation to the switching unit tocontrol the output of the common electrode voltages, thereby making thespeed of a bend alignment transition of a liquid crystal disposed in theLCD panel high.

Here, the LCD panel is characterized to have a liquid crystal with anOCB mode.

Moreover, at an initial operation, voltages applied to the commonelectrode line are characterized to be external bias voltages appliedthereto one time, and further characterized to be external bias voltagesrepeating on and off, and also further characterized to be voltages thateither the high-level bias voltages or the common electrode voltages arerepeatedly applied thereto.

A method of an LCD, which has a LCD panel with liquid crystal, a gatedriver, a source driver, and a back light unit, according to one featureto implement another object of the present invention comprise:

(a) forcibly stopping the gate driver and the source driversimultaneously as initially starting the LCD,

(b) applying high-level bias voltages supplied independently to thecommon electrode lines of the LCD panel to induce a bend alignmenttransition by a high transition difference;

(c) driving the gate driver and the source driver according as a certaintime has passed, and

(d) applying common electrode voltages to the common electrode linesinstead of the high-level bias voltages, and applying specific backlight driving voltages to the back light unit.

According to this LCD and the driving method thereof, at an initialoperation, by applying the high-level bias voltages instead of thecommon electrode voltages and stopping driving of the gate driver, thesource driver and the back light, the speed of the initial bendalignment may be highly increased in the LCD with an OCB mode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram to illustrate an operation of a normal OCB mode.

FIG. 2 is a diagram to illustrate an ON/OFF cycle of a normal OCB mode.

FIG. 3 is a diagram to illustrate an LCD for highly increasing the speedof initial bend alignment according to an embodiment of the presentinvention.

DEAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments will be described for those skilled in the art to practiceeasily.

FIG. 3 is a diagram to illustrate an LCD for highly increasing the speedof initial bend alignment according to an embodiment of the presentinvention.

Referring to FIG. 3, an LCD according to an embodiment of the presentinvention includes a DC to DC converter 50, a timing controller 100, afirst switching unit 210, a second switching unit 220, a gate driver300, a source driver 400, an inverter 500, a back light unit 600 and anLCD panel 700.

In general, an LCD module raises or reduces supply voltages required toeach of circuit blocks from a single supply independent of a notebookand its monitor, and then it generates required voltages to use it.There are supply units of the LCD module such as the DC to DC converter50 and the inverter 500 for driving the back light.

The timing controller 100 is provided with image signals R, G and Binputted from an external graphic controller (not shown) and controlsignals DE, MCLK, Hsync and Vsync for displaying the image signals,respectively. And then it outputs a signal for the gate driver 300 and asignal for the source driver 400, and provides a first switching signalS1 to the first switching unit 210 and a second switching signal S2 tothe second switching unit 220.

That is, at an initial operation of the LCD, the timing controller 100is controlled so that the outputs of the high-level bias voltages froman external device are applied to the common electrode lines of the LCDpanel 700 and the driving of the gate driver 300 and the source driver400 is stopped, thereby highly increasing the speed of bend alignmenttransition in the LCD with an OCB mode.

Then, the timing controller 100 is controlled so that the commonelectrode voltages to the common electrode line of the LCD panel 700 isoutputted, and signals for driving the gate driver 300 and the sourcedriver 400, and a signal for driving the back light are outputted. Here,at an initial operation, the timing controller 100 may be controlled sothat a high-level bias voltages are applied one time, bias voltagesrepeating on and off are applied, or bias voltages and common electrodevoltages are alternately applied.

The first switching unit 210 includes a first switch 212, a secondswitch 214 and a third switch 216 to switch output of the gate voltages,the data voltages and the back light voltages depending on the firstswitching signal S1.

More in detail, the first switch 212 controls signals Gate clk and STVfor driving the gate driver provided from the timing controller on thebasis of the first switching signal S1, and preferably, when the firstswitching signal S1 with OFF level is applied, the switch 212 stops theoutput of signals Gate clk and STV for driving the gate driver, when thefirst switching S1 with On level is applied, the switch controls theoutput of signals Gate clk and STV for driving the gate driver.

The second switch 214 controls signals HCLK, STH, LOAD and RGB fordriving the source driver provided from the timing controller 100 on thebasis of the first switching signal S1, and preferably, when the firstswitching signal S1 with OFF level is applied, the switch 214 stops theoutput of signals HCLK, STH, LOAD and RGB for driving the gate driver,when the first switching S1 with On level is applied, the switch 214controls the output of signals HCLK, STH, LOAD and RGB for driving thegate driver.

The third switch 216 controls signal B/L CONTROL for driving the backlight provided from the timing controller 100 on the basis of the firstswitching signal S1, and preferably, when the first switching signal S1with OFF level is applied, the switch 216 stops the output of signal B/LCONTROL for driving the back light, and when the first switching S1 withOn level is applied, the switch 216 controls the output of signal B/LCONTROL for driving the back light.

The second switching unit 20 outputs high-level bias voltages from anexternal device to the common electrode lines of the LCD panel on thebasis of the second switching signal S2 at an initial operation, andthen, it outputs the common electrode voltages instead of the high-levelbias voltages according as a certain time has passed.

The inverter 500 applies specific voltages for driving the back lightunit 600 disposed on one side of the LCD panel 700 depending on a backlight control signal from the timing controller 100. In general, theinverter 500 for driving the back light is combined with the LCD modulein the whole system as a form of separate module mounting parts such asa chauffer, a transformer, etc.

The LCD panel 700 is formed of a plurality of pixels made of m×n matrix,which drives related built-in pixel electrodes in response to the datavoltages D1-Dm provided from the source driver 400 by applying the gatevoltages G1-Gn from the gate driver 300 to the related pixel electrodes.In this case, since large voltages are initially applied to the liquidcrystal molecules with OCB mode built in the LCD panel 700, it ispossible that it takes a very short time to make a tilt angle of theliquid crystal molecules in the center of the liquid crystal layer 90°.

In particular, since the LCD panel is not provided with any voltagesfrom the gate driver or the source driver at an initial operation, itspixel electrodes are kept a floating state, and perform bend alignmentof the liquid crystal in the state that the high-level bias voltages areapplied to only upper plate electrodes. Also, its pixel electrodes areprovided with the data voltages from the source driver after a specifictime, preferably, 500 ms has passed, so that some images are displayed.

Although, as above, the first switching unit is prepared separately inorder to control the outputs of signals applied to the gate driver andthe source driver and the output of signal for driving the back lightwith ON/OFF, it may be disposed within the timing controller to performso.

Furthermore, although at an initial operation of the LCD, more indetail, at the same time of an initial operation, high-level biasvoltages from an external DC to DC converter as an example are providedto the common electrode lines of the LCD panel, the high-level biasvoltages may be generated on the basis of supply voltages provided tothe gate driver. For example, assuming that voltages for starting a gatedriver are 27 Volts, it is easy to those skilled in the art that raisingthe voltages to be applied to common electrode lines of an LCD panel cangenerate high-level bias voltages of 30 Volts.

As mentioned above, at an initial operation of the LCD with an OCB mode,in order to obtain a bend alignment transition at high speed, thedriving of the source driver and the gate driver is stopped, and thehigh-level bias voltages instead of the common electrode voltages areapplied to the common electrode lines, and hence the time of bendalignment of the liquid crystal can be much reduced.

Here, at an initial operation of the LCD, high-level bias voltages maybe applied one time, a bias voltages repeating ON/OFF may be applied, orbias voltages and common electrode voltages may be alternately applied,but, even though the bias voltages are applied one time, it is enough tohighly increase the speed of a bend alignment transition.

Although the present invention has been described with reference to thepreferred embodiments, it will be appreciated for those skilled in theart that versatile changes and modifications of the present inventioncan be made without departing from spirit and scope described in theaccompanying claims.

As described above, according to the present invention, at an initialoperation of the LCD with OCB mode, the high-level bias voltages arecontrolled to be applied to the common electrode line of the LCD panel,and the driving of the gate driver, the source driver and the back lightare controlled to be stopped, and, after an initial operation, specificcommon electrode voltages are controlled to be applied to the commonelectrode lines instead of the bias voltages, and the driving of thegate driver or the source driver and the back light are controlled to beperformed, thereby highly increasing the speed of a bend alignmenttransition of the liquid crystal at an initial operation of the LCD withOCB mode.

1-16. (canceled)
 17. A liquid crystal display comprising: an LCD panel;a source driver outputting image signals to the LCD panel; and a gatedriver sequentially outputting scanning signals to the LCD panel,wherein at the same time of power on, high-level bias voltages areapplied to a common electrode line of the LCD panel, and simultaneously,driving of the source driver and the gate driver are stopped and after aspecific time has passed, common electrode voltages are applied to thecommon electrode lines of the liquid crystal display instead of thehigh-level bias voltages and signals for driving the source driver andthe gate driver.
 18. The liquid crystal display of claim 17, wherein theLCD panel has a liquid crystal with an OCB mode.
 19. The liquid crystaldisplay of claim 17, wherein the high-level bias voltages are providedfrom an external device.
 20. The liquid crystal display of claim 17,wherein the high-level bias voltages are generated on the basis ofsupply voltages provided to the gate driver.
 21. A liquid crystaldisplay comprising: an LCD panel; and a back light unit to output alight to the LCD panel; wherein high-level bias voltages are applied toa common electrode of the LCD panel, and simultaneously, and the backlight unit is stopped, and after a specific time has passed, commonelectrode voltages are applied to the common electrode of the liquidcrystal display instead of the high-level bias voltages.
 22. The liquidcrystal display of claim 21, wherein the high-level bias voltages areapplied to the common electrode of the LCD panel at the same time ofpower on.
 23. The liquid crystal display of claim 21, furthercomprising; a source driver outputting image signals to the LCD panel;and a gate driver sequentially outputting scanning signals to the LCDpanel, wherein the high-level bias voltages are applied to the commonelectrode of the LCD panel, and simultaneously, driving of the sourcedriver, the gate driver are stopped.
 24. The liquid crystal display ofclaim 21, wherein signals for driving the source driver, the gate driverand the back light unit are outputted, respectively when the commonelectrode voltages are applied to the common electrode of the liquidcrystal display.
 25. The liquid crystal display of claim 21, wherein atan initial operation of the liquid crystal display, voltages applied tothe common electrode lines are high-level bias voltages repeating on andoff.
 26. The liquid crystal display of claim 21, wherein at an initialoperation of the liquid crystal display, the voltages applied to thecommon electrode lines are voltages that either the high level biasvoltages or the common electrode voltages are repeatedly applied. 27.The liquid crystal display of claim 21, wherein at an initial operation,the LCD panel is kept in a floating state.
 28. The liquid crystaldisplay of claim 27, wherein the LCD panel comprises pixel electrodeskept in the floating state until the liquid crystal substantially turnsinto a bend alignment.
 29. A method for driving a liquid crystal displaycomprising an LCD panel having a liquid crystal, a gate driver and asource driver, the method comprising: (a) forcibly stopping the drivingof the gate driver and the source driver simultaneously as initiallystarting the LCD; (b) applying high-level bias voltages suppliedindependently to the common electrode lines of the LCD panel tosubstantially induce a tilt angle of a liquid crystal molecules in acenter of a liquid crystal layer 90°; (c) driving the gate driver andthe source driver after a certain time has passed; and (d) applyingcommon electrode voltages to the common electrode lines instead of thehigh-level bias voltages.
 30. The method of claim 29, wherein the liquidcrystal display further comprises back light unit and the method furthercomprises forcibly stopping the back light unit simultaneously asinitially starting the LCD.
 31. The method of claim 30, the methodfurther comprising, after step (d), applying a specific back lightdriving voltage to the back light.
 32. The method of claim 29, whereinthe LCD panel has a liquid crystal with an OCB mode.
 33. The method ofclaim 29, wherein at an initial operation of the LCD, the voltagesapplied to the common electrode lines are high-level bias voltagesapplied once thereto.
 34. The method of claim 29, wherein at an initialoperation of the liquid crystal display, the voltages applied to thecommon electrode lines are high-level bias voltages repeating on andoff.
 35. The method of claim 29, wherein at an initial operation of theliquid crystal display, the voltages applied to the common electrodelines are voltages that either the high-level bias voltages or thecommon electrode voltages repeatedly applied.